1. Field
The present application relates to voice telephony, and more particularly to control and status signaling over voice channels, such as in third party call control scenarios.
2. Related Art
Voice telephony remains a major application of interest for business and personal use. In an example corporate setting, a telephony installation at a site can have a large number of users connected to a Private Branch Exchange (PBX) server, which can interface those users to a smaller number of outside lines (e.g., an E1 or T1 line) (a PBX can be implemented using a server with telephony cards for example). A PBX can interface with other servers and systems, such as one or more application servers that can provide enhanced services to devices connected to the PBX, such as mobile devices. For example, a PBX can interface with an application server over an IP connection, using SIP signaling. Services provided by an application server can include voice mail, single number reachability, call forwarding, park, and conferencing, for example. PBX systems also can communicate with each other over trunk lines, and packet networks, depending on implementation.
A PBX can perform services for a voice call, based on direction from an application server. For example, a PBX can initiate an outgoing call to a number specified by an application server using SIP signaling to the PBX. A PBX also can provide information about incoming calls to an application server. For example, a PBX can provide ANI information, to an application server, for a call incoming to the PBX, which may be provided a service by the application server. An application server can provide what are known as third party call control services to voice devices. In third party call control, an application server can control aspects of a call in which it is not a party. Such control can include controls such as transfer, remote mute, and so on. Where a data channel between the application server and a party to the call exists, then such commands can be signaled and acknowledged over that data channel. In the absence of a data channel, DTMF tones provided over the voice channel are used. Continuing to enhance a user experience even when using such DTMF tones is desirable.